In general, a corrugated-fin heat exchanger is widely used, which is constructed by arranging a plurality of flat heat exchange tubes parallel to one another in a horizontal direction between a pair of opposing header pipes, and joining corrugated fins between the heat exchange tubes. In a case where this type of corrugated-fin heat exchanger is used as an evaporator, condensed water (dew water) adheres to the surface thereof, which increases an airflow resistance, and further, inhibits heat transfer due to a resistance of a water film adhering to the surfaces of the corrugated fins. As a result, there arises a problem of decrease in heat exchange performance.
Further, in this type of corrugated-fin heat exchanger, considering the water retention property of the corrugated fins, it is preferred that the fin pitch be increased. When the fin pitch is increased, however, there is such a trade-off problem that the area of heat transfer on the air side is reduced. Thus, it is necessary to consider the fin pitch and the area of heat transfer on the air side.
In order to solve the above-mentioned problem, the inventors of the present invention have conducted extensive study, and eventually proposed such a drain structure that water flow passages are formed by obliquely cutting and raising flange portions extending along end portions of each heat exchange tube in a width direction thereof, and are provided at an appropriate pitch in a longitudinal direction of the heat exchange tube (see, for example, Patent Literature 1).
According to the technology described in Patent Literature 1, the water flow passages for inducing water retained between the corrugated fins adjacent to an upper side and a lower side of each heat exchange tube are formed by obliquely cutting and raising the flange portions, and thus the condensed water (dew water) adhering to the surface of the heat exchanger can be drained.